Electrical transmission system



15,. 1942. w. B. sNow ELECTREL TRANSMISSION SYSTEM 'Filed oct. 15. 1941 /M/ENTOR W. B. SNOW By ATroRA/Ey Dec. l5, 1942. w. B. SNOW .ELECTRICAL TRANSMISSION SYSTEM i?. Sheets-Sheet 2 Filed oct. 15, 1941 u ummm www .mx 5S u ummm IIH` da. .Cu l 4 SS www Zt l .ba Y. Qmm .u Owr www@ rm@ h rbb um )mm F w.. S .Cu uw Si okt w fm@ fwn du. gmk www F Q Esi f Nm lkw .S Si (n (m, nu Qwklllll. w ummm Cum .Si L Dit Y 51W v mm f2 N @Pi ll. w w Y l l, SG l us l wl f nx #su 2;. .Sx atx n Nv fnv (w 6v r2.. fw. a

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Patentedv Dec. l5, 1942 nieuwe ELECTRICAL TRANSMISSION srs'rlzitrA o william' B; snow, summit, N. J., signor to Bell Telephone Laboratories, York, N. Y., a corporationjof NewYork Incorporated, Ne

Application october 1s,194-1,seria.1 -N0.415,o4s

' Y' scams' (c1. 17a-100.3) -Y This invention relates to electrical transmission systems, and particularly to systems4 in which the volume range of thesignal currents is compressed before transmission and expanded after reception. The invention Vis applicable to systems using Wire, cable or radiochannels over which the signal currents are transmitted 'for immediate reproduction, and also tosystemsin which vthe signal'currents are recorded for subsequent reproduction.

y The object of the invention'is tofautomatically the recorders and reproducersmay be repli'tceciby wire, cableor radiochannels.

Inthedrawingsi f, Fig. l .diagrammatically shows the invention embodied in.` a, film sound` rerecording system, with a. monitoring reproduceryand A f Fig. 2 diagrammaneany shows the mention embodied .in a theater reproducing system.

rcompress and expand the volumerangeot the transmitted signall currents under the control.y of an alternating currentvarying in amplitude 'in accordance with some function of the variations im amplitude of the signal currents', to arbitrarily further expand the volume range of the received currents under 'the control of thesame,.or asec- 1 ond, alternating currentl varying in amplitude, and to control the frequencyv characteristics,

reproduced currents under the control of a change in frequency of onefof the alternating currents.

A feature oi' the-invention is the use of alter-` nating currents, varyingin amplitudefwithout apr20 spatial distribution or `scenic surroundings ofthe preciable change iri`frequency,l to exercise .oneY

type of control of the transmitted signal. currents,

and also varying in frequency without'appreciable change in amplitude, to exercise another type of control over the reproduced signal currents, or

the conditions under which thefcurrents arereproduced.

. Another' feature of the invention isfthe use,fin a multichannel system, such asa stereophonic system,l of alternating currents of readily distinguish-l able frequencies, individual to each channel, for

controlling the automatic compression and ex` pansion of the volume range of thesignal currents; of other alternating currents of frequencies readily distinguishable from each other and from the rst currents, individual to each chan-4 nel, for arbitrarily varying the expansion of the volume range of the signal currents; the latter] currents being individually variable in frequency within ranges readilyv distinguishable from all the other currents; al1 of said currents .being transmittedv over a single channel separate from the channels transmitting the signal currents. I

For convenience of description, the invention has been disclosed as embodied in a three-fehannel illm sound recording and a lm sound reproduc ing system, but the 'invention is not thereby limited to these specic systems, as any type of re cording and reproducing system may be used, or

In my copending application,SerlalNog 328,078, tiled April 5, *1940, amultichannel transx'nission system isdisclosed'in whichfthe volume range of ythe signalcurrents lin 'each channel is automatically compressed under thecontrol of an alter-'- nating current havingra frequency individual to thechannel.- The vcompressed outputj of 'each channel is individually transmitted orrecorded. while ally ofthe` control currents. are transmitted or recordedina'commonchannel. o

In Fig. l'. of ,the presentldrawings, kthefliilm, l

` symbolically represents the recorded output of one ofthe channels disclosed in my` copending application Serial No.f32, 078,while the film Zsym- .bolically represents :j common.. record of all of the controlchannels.' 4'In a multichannel system there twill, of` course, be v'al record andy channel, as

shown `associated with therecord |ffor each. of the two ormore channels concerned. The record l of the compressed signal currents from a single channel, ,and the record y2 of all ofthe control currentshave, for convenience, `been showlnas on separate films but it will belunderstood that all,

orvany number kof these. records may becombined upon acommonglilm.,rv The records vl andi` 'are Y driven in synchronism at constant speed inthev K usual manner by knowndrve: mechanisms, fnot shown. f l

. Light from a suitable source isfprojectedin the lusual manner through the record `I to excite a photosensitive device 4 to produceA an electrical current varying in accordance with the original compressed signal currents. Similarly, light"from va. suitable source 5 is projected through thefreeord 2 tobexcite a photosensitive device 6 toproduce currents varying in 4 accordance vvith the con. trol currents used to produce fthe compression.

.When some other type `of 'record'.is; used, the'appropriete pick-up devicewill be substituted'for the lightsourcesand photosensitive devices dis- A closed. yIf awire,A cablegor radio link be substitutedlforthe recording and reproducing linlqthe' y outputs of these channels will replace the outputs of the photosensitive devices 4 and 6.

VThe output of the photosensitive device `{suitably amplified in theraxrnpliers 1 and 8is rere; corded on the record 9.driven at constant speed v amplitude of Ythe currents constant.

in synchronism with the record I,k in the usual 1 manner. Similarly, the output of the photosensitive device 6, suitably amplified in the ampliilers Illand II, is rerecorded on the record I2,v

driven in'synchronism with the record 2 by known means.

Y Though, for convenience, the records 9 and I2 have been shown asvseparate records, it is evident that these records may be combined upon acommon medium.

The amplifiers 8 and I I may, if desired, include ,means for limiting the output, so that the recorder y f is not overloaded. l ,Y

vA portion of the output ofthe amplifier i is also supplied to the amplifier vI3 thence throughv the automatic expander Il, the. devices I5 and I6 tobe explained hereinbelow, and, ifd'esired,

a 'further amplifier I1 lto the'reproducer I8, yor other utilization device. When the system is used for the immediate l currents of the frequencylgenerated byv the'oscillator 22 under the control of thedevice 26, 'or it may be adevice of thenature of the discriminator in a frequency lmodulation receiver, jin which the output amplitude is vdepe'ndentV upon the frequencylof f the currents supplied tothe input, thus giving fine gradations to the control of the quality .of the transmittedsound currents. The currents passed `by the frequencyfselective circuit 21, or a rectifiedrcomponent thereof,

supplied to relays, or other suitable devices, associated withthe quality control networkY I6 Yir-,the

' present channels, and f also to other relays, or]` controlling devices,"associated with similar qual-l i ity control networks in the,y other channels.

quality control network IG-is of thenature of av l tone Vcontrol network, orI other equalizer, which A modies in any desired manner, the response frereproduction of the signal current, -with a-wire, l

cable or radio channel attached-to the input `of,

the amplifier 1, the rerecording machine 9 may be eliminated, the output of the amplifier .8 being supplied directlyto the amplifier/I3. j n

A portion of the output of theampliiier kII is supplied to the amplier'l9,"thence to fa filterv v20,

which selects thecontroljcuxrentindividual to the particular channelshown, and supplies this control current to the expander rectifier 2|-, the

outputjof which controls theautomatic expander Il, to Aexpand the volume rangerof the reproduced signal current vto the range of the original signal currents, as described in my copending y application Serial No. 328,078'. l A The output of the amplifier other channels.` 2 Y A'n oscillator 22 generatiesan alternating "curbrent of reason'ably*con'stait amplitude and frequency D, which is supplied through the manu'- current is also supplied through the amplifier I9 andthe filter 2l to the rectifier 25 which controisthe manual expander I5in the reproducing "circuitto' produce an arbitrary enhancement of vthe amplitude of the` .current reproduced by the reproducer I8,y as describedin United States Patent 2,254,034-, August 26, 1941', H. Fletcher.

I9v'is also supplied v to other filters which select the appropriateconfitrol frequencies, designated frequencies B 'and C, which control the automaticexpansionl the Y allyvariable attenuator`23, toiA thelrecorder con n operating with the record I2.l Agportion of Vthis v'A manually operable device4 26 controls a switch, relay ror, other device, rassociated with the oscillatorv 22 to change thefrequency generated by thezoscillator', without changing the amplitude of the current generated by the oscillator. This relay, or other Aswitching device,'may `change the frequency of the oscillator 22 in-known manner by changing the inductance, resistance or capacitance in the oscillating circuit, and may, if necessary, also control an attenuator connected to the output ofthe oscillatorY so as to maintain the This current of changed frequency is recorded on'the record I2 and is also supplied through the amplifier `I9 tothe filter 2L The filter 24 isa conventional band'pass"filter,which will pass quency characteristic of the channel. The curevk rents from the network 21 operaterelays, or other f controldevices, to modify the value of the components in the quality control network I,or`jto switch componentsintov or but of the circuito! the quality controlnetworlr.` '1 J The oscillator 28. generates a current of` rea,k

sonably constant amplitude and frequency which is suppiiedthrough the manually.'variableatteufr uator 29 and.recordedon the record"`I2.` {Apor tion of this current` is supplied a through thel amplifier I9 to thek lter 30 and the 'rectifier` Il which controls a manual; expander, similar 4to the expanderIS, in one of,` the otherchannels ofthe system. 1

' `A manually oper vbledevice 32 controls devices associated with the oscillator 28 to changel the l frequency of-ithe oscillator; 2lil in amanner simi@A` Y lar to thechange inv the frequency `of theloscil- [l i iator 22 ,causedbyoperation of the device 28.1r

The current' of Achanged frequency from the" oscillator is recordedon-the record Izfandis also {supplied'through the amplifier` l 9 antipassefik I by the filter-30 to vthe vrectifier 3l and:. ..also

through. the' frequencyselective circuit 'lljtoql` stepping switches, lrelaygroups or gvariable, `Sitin A devices, arranged to switch the reproducersasso- Vciated-witheach of the'channels., l l

The lter 30,. `1ike the filter 2l. will passeurrents' havingV all of` the frequencies generated ,by

theA oscillator A28, but rwill not'pass any 'ofthe other control currents.` ,'I'h'efrequencyf'selective circuit 33, like the frequency selective circuit 21, willr not,V pass current of the `original frequency generated bytheoscillator20, but'will passeur@ rent of the frequency generatedv by the oscillator` V28 under thecontrol of the manuallyoperable device 32, or' may Vfunction `asa discriminator in the manner discussed .inconnectionwithfcire f all of the'currents of thefrequencies generated y ,'by` the oscillator 22, butwill reject all of the other control-currents.

The'frequency selective circuit 21 may be .of

the nature of a conventional band-pass filter which will reject currents of the frequency originally generated by the oscillator 22, but will pass Y In a similar mannenthe oscillator generates a current, which is recorded on the record I2, of a frequency which will pass through the` filter 35 to therectii'ler 36 controlling the expanderin the thirdchannel.. Whentheffre'-V quencyMof the oscillator 31,4`is changed bythe manually ,operable device `31,"the currents `of `changed frequency are passed .by thefrequ'ency Y selective circuiti, which vis similar to the circuit 21 andl 33, tol operate a selector 39 whichmay` control Athelights or scenery associated with the `reproducers III.

The record I2 willhave in a single trackthe records of the currents of 'thefrequencies vAfl?, I

andC, respectively varying in amplitude in' accordance with the automatic compressionlof the volume range of the signal currents in therespecaccesso be omitted, and the system koperated only with the manual enhancement, and the control of the n tive channels, and will also have records of the currents generated by the oscillators 22, 28 and 34, normsally having the frequencies D, Eand F, or the corresponding frequencies as modified by the manually operable devices 26, 32 and 31, varying in amplitude in accordance with the enhancement appliedby the attenuators 23, 29 and Fig.-2 discloses a reproducing system, such as atheater system, using the records produced by` the rerecording machinein Fig. 1, or a print or duplicate thereof. For convenience, the records ofthe signal currents from the various channels have been shown on a ,film separate from the film carrying the records of the-various control currents, but, these records may be separate tracks upon the same film.

yLightfrom a suitable source 4l inthe usual manner through the -record on the film 42 and excites the photosensitive device 48. The signal currents in the output of the photosensitive device 43 are amplified in the amplifier 44, automatically expanded in volume range in the/expander 45, arbitrarily expanded in yvolume range in the expander 46, modified in wave form in the quality control circuit .41, further amplified inthe power amplifier 48, and reproduced by the selected reproducer 49.

Light from a suitable source 50 is projected in the usual manner through the record of the control currents on the filmv 5I to excite a. photo--` sensitive device 52. l

The filter 54 selects from the output of the amplifier 53 the current having a frequency A corresponding to the automatic compressionapplied to this channel, and supplies this current to a rectifier 55 which controls the automatic cxpander 45.

Filters, corresponding to the filter 54, respectively select currents having frequencies of the automatic compression currents corresponding to channels B and C and supply these currents to circuits controlling the automatic expanders in these channels.

Filters 56, 58 and 60 respectively select currents having the frequencies D, E and F and supply these currents to the control circuits 51, 59 and 5I, respectively controlling the manual expander, such as the expander 46, corresponding to each of the channels. I

quency selective circuit 62 to control the quality control network, such as network 41, in each of the channels. 7,'

When the frequency E of the current selected isv projected conditions surrounding the reproduction.

What is claimed is:

1. In a transmission system, a source of signal-` waves, a load circuit, va transmission channel' from said source to said loadcircuit, means in said channel for expanding the amplitude range of the transmitted waves, a source of alternating currents, a manually operable att'enuatcry connected to said source, a. frequency selective cir-l cuit for supplying current from saidjsource to said expanding means under the control of said attenuator, means for changing the frequency of said alternating currents, a second frequency selectivezcircuitarranged to reject the currents from said source of the original frequency and to l,pass the currents from said source of the changed frequency, and means associated withsaid chan- I nel actuated by the currents passed by said second frequency selective circuit. ,v y

.l v2. In a transmission system, a 'source of -signal waves modified in' amplitude, a load circuit, a transmission channel from said source to said load circuit,` a source of. alternating currents of constant frequency varying in amplitude in accordance with the modifications made in the Ysignal waves, means in said .transmission channel under the control ofj said latter currents for restoring said signal waves to their originalamplitude, a second source of alternatingl currents, a manually operable attenuator connected to said source, means in said transmission channel `for expanding .the amplitude range of the Vtrans'- xnitted waves, a filter and rectifier for supplying current fromrv said second source to said latter expanding means under the control of said attenuator, means for changing the frequency of said alternating current, a second filter arranged to reject the current from said source of the originalfrequency and to pass thel current from said source of the changed frequency, and means as- Y.

sociated with said channel actuated by ithe'rcurrents passed by said second filter.

`.3. In a sound reproducing system, a source of sound currents modified4 in amplitude, a sound reproducer, a transmission channel from said source of sound currents to said sound reproducer, a source of currents of constant frequency varying in amplitude in accordance with the modifications made in said sound currents, means in said transmission channel for compensating the modications in said sound currents under the control v of current from said latter source, means in said f transmission channel for Aexpanding the amplitude by the network 58 changes fromits normal value,

this current of changed frequency is selected by the frequency selective circuit 63 and transmitted, to the switching devices in -the various channels controlling the selection of the reprorier currents of the frequencies A, B, C, it is evident that these latter currents and their function may be omitted if desired. Inother words, the automatic compression and expansion may range of the sound currents, a source of alternating current lvarying in amplitude in accordance with desired changes in the amplitude of said sound currents, a lter and rectifier for supplying current from said latter source to said .expanding means, and a second filter connected to said latter source and arranged to reject the current from said source of one frequency and to pass the current from said source of another frequency,

and means associated with said channel actuated by the current passed by said` second filter to modify the condition under which said soundv currents are-reproduced.

4. A composite sound record comprising a plurality of records in separate tracks of a plurality of sound currents modified in amplitude, and a plurality of records in a single track including records of carrierrcurrentsrespectively varying in.

amplitude with the modifications in the amplitude of said sound currents, and a plurality of records oi' carrier currents respectivelyl varyinginampiifj ture with desired additional modiiications inthe amplitude of said 'sound currents, and, atvtimes; changing in frequency in accordance with `desired changes in thegconditions under whichsaid `sound n ascenso v s lcontrol'r means in 'serialrelationship:freer'n iztively Aconnectixig -each pick-upto the; corresponding" Y currents will ybe reproduced. allof` saidv carrier n currents'beln'gfoi different and distinguishablev frequencies. s

`5`. In a sound rerecordingxsystem;arecord: of

sound currents modified in amplitude,` meansl for:

reproducingand rerecording 'said' recordga 'rxioni-V toring sound reproducer,` a transmissionchannel from said recorder to said sound reproducer, an

automatic expander,V a manual expandenand afl i quality controlwcircuit "in seriesfrelationship in said .transmission channel, 'a record oijafcurrent I .of constant Irequencyfvarying in amplitudein akii.

cordance with the modicationskinthe amplitudes` oi' said` sound currentst means'for reproducing* said latter record, means for' rerecording 'the jcurmodiilcation's in thefamplitudesoi the sound currents, a source of alternating current, a

s mations .to be made'inmasound-eurfehtsga n lat' times, 4changing ,.imfrequency,vritiioutf-` cl'ianefv in amplitude miv/accordance with'deairedixchangeskv in v'theconditionaurideryshichsilid sound willibe reproduced: allot/.said 'carriercurjen b'e operable jattenuator connected 5to l said Isource;r

means for supplying'current from said' attenuator to said rerecorder. 'a lte'n and rectiner -forsupplya *I 11M current ,from SaldSoicej misma manuiu ex; 1 pander in said transmission channel .under the control lo! said attenuaton'means for changing vmi; or mneremvandfmsungmsmbie requeridas, 8. In asoundl reproducirigsy's,texn. V .medium the frequency `of=the alternatingcurrentslirom said source; a second flter 'arrangedtorejectfthe currents from saidl source of `theoriginal` fr-` 'quen'cy and to pass'the currents from rsaid'source ofthe changed frequency, and means connected l to the output ot saidl` second filter lfor, controlling saidquality control network inf said transmis-` sion channel." fi' i l l u.

6. `In a'soundre'producing"system;'a recording medium having 4a;1,.lura.lit1,f` of records of sounds modied in amplitude and separate records `of a plurality of carrier currents, a pickup device infdividual to each'of raid sound records, a sound reproduces individual to each oi said' sound records, a transmissionrchannel containing *twol vcontrolling one of 4the control 'means'rin said ofsoundlcurrents; and.- a` plurality off-records in a:

y20 f 4Vrents, reproducedfrom said'latter record.'l a filter e connected to said rerecorder transmitting current to said automatic expander tov compensate `the l v laiclriup` to'tl'ieycrresriponding.reprodu` mon pick-up forall1"said carriercurrent records;`

n riet current for controlling Vthe `second` control means in said channel.` f

reproducer, a common'pickj-up lfor all said carrier-g rentcorresponding to a giyen channel and'for Y e;

channel withssaid current, means Ivor'selecting-,` frornthe output` of saidicommonpick-upsccnd carrier current corresponding'fvtoag'iy nel and for controlling the. second cont] l ij Vmv-said'channel by variationsin vthe amplitude ofjsaid current; and means responsive to achanfge fm the frequencygof endommager-:entf greep e trolling thefconditio tion ofthe Kp A i f` .e l l'1,V A compositelsound recordcomprlsins @PluieYk ralityzox recordsfinjseparategtracks offafrplurality single vtrachfoi! ff'carrier .Jvcurrentsrarespectiycl'. varying 1n ampntuae with aesrreuarmtmf 4having a -pluralityoiffreeords ot 'sounds'and aplus' rality otrecords'ofcarrierlcurrents pick lppfo each of said'sound recordalait-soun r'eprodu er forA eachv of;v saidv` sound`jreoord's, `trnl,l`ii$io u y channels each'containingitwdcontrolfmea serial relationship frespectivelyf'connectin L' Q means for selectinglfrorn the outputof's'aidcom mon pick-up acarriervcurrent correspondin given channel'and for controllinggon'e; control` means in said 'ch'annel by variations'i-in e the amplitude 'l of` saidV current, `and: meansjre sponsive" to sa. change in the frequency of saidcafr` 

